Herpes simplex virus-1 (HSV-1) is human alphaherpesvirus that establishes a lifelong latent infection in peripheral nerve ganglia following primary infection. HSV-1 infections are generally benign, although its capacity for neurovirulence and neuroinvasiveness are the primary mechanisms through which HSV-1 can cause harmful disease in humans, especially in neonates and immunocompromised hosts. Our overall objective is to develop a model for examining HSV-1 neuropathogenesis in human sensory ganglia in vivo. We will evaluate HSV-1 infection of human dorsal root ganglion (DRG) xenografts in mice with severe combined immunodeficiency (SCID), exploiting the system that we created to investigate varicella- zoster virus (VZV) neuropathogenesis. The biology of HSV-1 infection is similar to VZV in that both HSV-1 and VZV establish latency within sensory ganglia following primary infection. Studies of VZV in the SCIDhu DRG model have provided the first opportunity to examine replication of a human alphaherpesvirus within cells that comprise human DRG in vivo. The DRG xenograft model has the potential to reveal characteristics of HSV-1 neuropathogenesis in the natural human host tissue microenvironment in vivo in an experimental system that will add substantially to observations from rodent models. Experiments will address three specific aims: (1) we will define the course of events that follows HSV-1 inoculation of human DRG xenografts in SCID mice, identifying what cell types within DRG are permissive for HSV-1 gene expression, whether neurons and/or satellite cells become productively infected and whether HSV-1 undergoes the pattern of transition to persistence in human neurons that we have observed in VZV-infected DRG xenografts;(2) we will investigate HSV-1 gene functions through the evaluation of recombinant HSV-1 strains, in particular we will examine the requirement for HSV-1 thymidine kinase (TK) during initial infection and persistence in DRG, and gD mutants for their capacity for viral entry;(3) if HSV-1 is shown to establish persistence in DRG xenografts, we will assess whether this model can be used to study HSV-1 reactivation by explanting latently-infected DRG xenografts and treating with agents that trigger neural cell signaling pathways and increase HSV-1 reactivation in rodent models. This work is intended to demonstrate the feasibility of using DRG xenografts in SCID mice to explore the molecular mechanisms of HSV-1 neuropathogenesis in differentiated human sensory neurons and non-neuronal cells within their sensory ganglia tissue microenvironment in vivo. In addition to new insights about basic virus-host interactions, such a model has potential value for studying antiviral drugs and live attenuated HSV-1 vaccine candidates to treat or prevent human disease caused by this common virus. PUBLIC HEALTH RELEVANCE: Herpes Simplex Virus 1 (HSV-1) causes oral and genital lesions and encephalitis. These infections remain an important public health problem in the United States. Serious complications from HSV-1 can occur in healthy people and in those who have diseases that impair their immune systems. Our goal is to develop a model to study how HSV-1 infects human nerve cells that will have potential value for developing new drugs and vaccines.